Ankle sprains are the most common injury in sports; the lateral ligament complex of the ankle is most often injured, and approximately one-quarter of all reported sports injuries occur in the foot, among which about one-half are sprains. In addition, ankle sprains account for 10% to 15% of all time lost to injuries in football on the professional, college, and high school levels, with the average player losing five weeks. Ankle ligament injury is also the most common injury in modern and classical dance.
Current methods of determining degree of ankle joint instability, i.e., ankle joint laxity include a stress X-Ray technique of the Talar Tilt. The disadvantages include the time consumed in producing and reading an X-Ray, the relatively high cost, the complexity and the exposure of the patient to X-Radiation.
The manual anterior drawer test comprises a trained person--orthopedic surgeon or other medical professional, pulling upon the suspect ankle to note laxity in the ankle ligaments. Here again, the disadvantages are unreliability and variability within and between doctors and patients.
The present invention provides a method and an improved apparatus for quick, reliable, reproducible, low-cost and risk-free ankle joint laxity measurement which is also very low in variability both intra- and inter-observer.
Reliable orthopedic joint laxity measurement is an important component of orthopedic injury diagnosis, particularly for knee and ankle joints and particularly because knee and ankle joints are frequently injured by people engaging in sports. An orthopedic surgeon who evaluated knee injury prior to the present invention typically may have used a prior art device known as a KNEE LIGAMENT ARTHROMETER.RTM. manufactured and sold by MEDmetric Corporation, 4901 Morena Boulevard, Suite 322, San Diego, Calif. 92117, and protected by U.S. Pat. No. 4,583,555. The KNEE LIGAMENT ARTHROMETER.RTM. in common use is known as the Model KT 1000.TM..
The KT 1000.TM. is the prior art upon which the present invention is an improvement on both the apparatus and the method of use.
The MEDmetric Corporation teaches that its KT 1000.TM. is to be used for measuring and assessing the integrity of only the ligaments in the knee of a patient being examined. MEDmetric teaches away from the present invention in that the present invention embodies a method of use of the KT 1000.TM. for ankle laxity measurement and is thus specifically disapproved taught away from by MEDmetric.
While MEDmetric teaches use of its KT 1000.TM. only for the knee, the present invention teaches use of the KT 1000, with appropriate novel modifications as herein presented and described, for use in measuring the laxity in the ankle joint.
The ankle joint, like the knee joint, is a point of frequent injury, and in particular, sprained and twisted ankles and ankles with more serious ligament injuries need diagnosis as often, if not more often, than injured knee joints.
Thus, the novel method of use of the modified KT 1000.TM. represents not only novel apparatus modification to the KT 1000.TM., not only a novel method of using the modified KT 1000.TM., but also a greatly expanded use for the modified KT 1000.TM. in that ankle injuries, as a new category of injury, will be added to the utility of the newly-modified KT 1000.TM..
In so doing, the present invention addresses a long-felt need in the art of orthopedic diagnosis of ankle joint injury, namely, to standardize and to make quick, convenient and most important, reliable, the assessment and diagnosis of injury to the ankle joint. This is especially important in view of the large number of ankle-joint sports injuries which are currently being treated.
The type of injury for which MEDmetric teaches that its KT 1000.TM. is useful is in diagnosis of injury to the knee in which the cruciate ligament(s) is (are) injured--by tearing, hyperextending, or otherwise. Cruciate ligaments are structures which are specific to the knee.
Injury to the cruciate ligaments often manifests itself in the laxity of the cruciate ligaments, which laxity, in turn, results in the tibial bone having more relative translational movement ability than would be available to the tibial bone in a normal healthy knee.
Because the tibial bone is able to wobble in a knee where the cruciate ligaments are compromised, a knee with injury to the cruciate ligaments may be termed unstable by an orthopedic surgeon. The person afflicted with this kind of cruciate ligament injury is not going to be able to rely on the firm placement of the tibial bone.
The injured person may thus experience a tibial wobble characterized by an inadvertent, unwanted and uncontrolled mis-alignment of the tibial bone in relation to the knee while the knee and leg are under stress, as during a standing, walking or sports-playing activity. The misalignment, resulting from the wobble, predisposes the person with the injured knee to further injury and/or re-injury.
The KT 1000.TM. is an instrument specifically designed for use by an orthopedic doctor to measure the degree to which knee ligaments are lax, thus permitting at least the possibility of a potentially dangerous tibial wobble. If the knee ligaments are more lax than they should be, the tibia will have the ability to travel anteriorly or posteriorly when an examining doctor applies force in the respective anterior or posterior direction to the calf of the patient, since the tibial bone is in the calf.
If the tibia is permitted to travel more than a healthy distance in an anterior or a posterior direction, knee ligament laxity, and thus knee injury, is indicated by the fact of the anterior or posterior movement.
Diagnostic measurement of ankle joint laxity is an important part of the novelty of the method of use of the present invention. In the ankle joint, injury to and laxity of the following ligaments, in the following order is involved: (1) the anterior talofibular ligament; (2) the calcaneofibular ligament; and (3) the posterior talofibular ligament. It is in that order that the ligaments of the ankle fail under the stress of an injury such as an ankle sprain. The least serious ankle injury involves compromise only to the first, anterior talar fibula ligament. Progressing, injuries of increasing severity will compromise the calcaneofibular ligament second; and finally, the posterior talofibular ligament will be compromised in the most severe ankle sprain.
With any or all of the foregoing ankle ligaments compromised, the ankle joint will be permitted forward, or anterior movement. The more lax the ligaments, the greater the anterior movement will be noted by the examining doctor. It is reliability, reproducibility, comfort and convenience to ankle joint laxity measurement that the method of the present invention provides.
Because of the configuration of the fibula and the calcaneous bones, forward or anterior motion of the ankle joint will depend upon the joint being adjusted so that the foot is slightly bent-down. Orthopedically this condition is known as joint flexion. When the foot bends downward from a neutral position, the flexion is called plantar flexion. Thus, with an optimal degree of plantar flexion, experimentally found to be about 10.degree. from the neutral position, ankle joint laxity can be reliably and accurately measured according to the present invention.
The usefulness of a machine, as compared to an examination performed by a doctor, orthopedist or surgeon using the hands alone is that a machine is capable of giving reliable indications of both force applied and the differential displacement of the joint in the case of knee joint examination. Thus, an important part of the problem solved by the novelty of the present invention is the introduction of instrument reliability and reproducibility to the diagnosis of ankle joint injury and the measurement of ankle joint laxity.
While The KT 1000.TM. machine represents an effort to standardize diagnosis of cruciate ligament knee injury and is thus advantageous over the less reliable subjectivity of non-instrumented diagnosis, the KT 1000.TM. also has disadvantages. To begin with, the KT 1000.TM. is designed for contact upon and measurement of the knee joint only.
Consequently, the KT 1000.TM. has structures for contacting the anatomy of a patient being examined which are specifically named for the body parts which are to be contacted. The KT 1000.TM. has two tabular anatomical reference pads, which MEDmetrics respectively calls the patella sensor pad and the tibial sensor pad, based upon the fact that when the KT 1000.TM. is put in use as taught by MEDmetric, the patella sensor pad is placed in contact with the patient's knee (patella), and the tibial sensor pad is placed in contact with the anterior aspect of the proximal tibia, in other words, on the front (anterior) portion of the lower leg below the patient's knee.
It is a disadvantage to name the anatomical reference pads by the specific anatomical structure to which they are applied because when the modified KT 1000.TM. is used in the present invention, the ankle, and not the knee is measured for laxity and the anatomical structures are different in the ankle than in the knee. Therefore, the present invention calls the sensor pads anatomical reference pads.
In the present invention, as well as in the prior-art KT 1000.TM., the sensor pads are capable of moving laterally in relationship to each other. The prior art KT 1000.TM. measures relative translational movement of the tibia in the anterior and/or in the posterior direction. The more movement, the greater the degree of laxity of the knee joint and thus the greater the severity of the injury being diagnosed.
Such relative translational movement is produced in the prior art KT 1000.TM. when the examining doctor applies differential force to the patient's tibia by exerting a pulling force in an anterior direction or a pushing force in the posterior direction on the handle provided for that purpose in the prior art KT 1000.TM.. The patient's tibia, if it can move anteriorly, will cause anterior directional movement in the tibial sensor pad of the KT undergo posterior translational movement.
Thus, the tibial sensor pad will experience relative anterior movement or relative posterior movement of a certain number of millimeters relative to the patella sensor pad. The greater the anterior or posterior distance traveled, the greater the knee joint laxity.
The examining doctor's concern in using the prior art KT 1000.TM. is to ensure that the KT 1000.TM. is properly positioned and aligned on the knee of the patient, and to observe and record how much anterior-direction force or posterior-direction force is used and how much instability exists in the knee joint as determined by the number of millimeters of anterior or posterior travel, also called translational movement, is available to the tibial bone.
Unfortunately, other major disadvantages exist in the prior art KT 1000.TM. surrounding the crucial functions of observation and data recordation by the examining doctor. The prior art KT 1000.TM. is provided with a dial-type analog indicator for showing the relative distance of reference pad travel.
The prior art KT 1000.TM. analog dial is marked in increments representing millimeters of pad travel, and a rotary indicator turns clockwise or counterclockwise to indicate the direction of relative pad movement, with the magnitude of distance indicated by the arc traveled by the dial indicator, which sweeps out a given number of millimeter increments. The prior art analog distance indicator is zero-adjustable.
But the disadvantage in this analog dial-type distance indicator is the fact that the examining doctor must keep his or her eyes vigilantly upon the dial to note how much movement, i.e., how many millimeters, are traveled by the reference pads, and thus by the tibia under examination. When the examining doctor releases his or her anterior-direction pressure upon the handle of the prior art KT 1000.TM., the patient's knee joint immediately resumes its pre-examination position.
Unfortunately, when the patient's knee resumes its position, so does the analog distance indicator on the prior art KT 1000.TM., and if the examining doctor failed to note the very brief extent of the arc swept by the analog indicator, the doctor will have to repeat the pressure test.
A further disadvantage of the prior art KT 1000.TM. is the fact that the examining doctor may apply pressure in an anterior direction by pulling the handle of the KT 1000.TM. provided for that purpose--but the doctor has no way to know how much pulling pressure is being applied until a force of 15 pounds, or 67 Newtons (N) is achieved, at which time, the prior art KT 1000.TM. sounds a horn. Upon further application of 20 pounds (89 N) of anterior direction force, a second, different tone is sounded by the KT 1000.TM. horn to alert the examining doctor to the amount of force being applied.
Not only is there no available measure of smooth and continuous application of anterior force, against which knee joint laxity may be measured, but also, the sounding of the horn is likely to frighten the patient. And there is no way for the examining doctor to know how far above 20 pounds of anterior force he or she may have applied, and further there is no way for the doctor to know how much force was applied above 15 pounds but below 20 pounds, since the 15-pound horn will sound at any applied force level at or above 15 pounds but below 20 pounds.
Indeed, in product literature, MEDmetrics president K. R. Watkins states that "t!here are several factors other than instrument accuracy which may affect displacement measurement. Physiological variation, tester technique, conditioning of patient, pretesting activity and apprehension of the patient are a few of these." emphasis added! Watkins, K. R., introductory remark dated June, 1990, San Diego, Calif., included with KT 1000.TM..
The product literature referred to comprises reprints of several studies, which product literature is collectively called Knee Stability Measurement Using the KT 1000.TM. Knee Ligament Arthrometer.RTM. A collection of studies printed in journals compiled by MEDmetric Corporations, manufacturers of orthopedic instrumentation including the KT 1000.TM., and dated San Diego, Calif., June, 1990.
It would be a great advantage to be able to note not only how much anterior joint movement is present, and thus how lax the joint is, but also to know how much force was needed to produce the anterior joint movement. If, for example, two patients show anterior movements of, say, 4 millimeters, it may also help the examining doctor to know whether 3 pounds, 5 pounds, 10 pounds, 15 or 20 pounds of anterior direction force were required to produce the 4 millimeter movement.
If less force were required to produce the same movement, then both force and movement should be taken into account in assessing joint laxity. The same movement produced by less force indicates a more severely injured and thus less stable joint--since it is ultimately the patient who will be applying the pressure of normal or rehabilitative effort to the joint being diagnosed.
The present invention solves the afore-described problems of the reversible analog dial-type distance indicator requiring intense observer vigilance, the problem of the inability to note or to measure force other than at 15- and 20- pound discrete levels, and the problem of patient fright by the prior art KT 1000.TM. force indicator being provided in the form of an audible horn with different tones for the 15 and 20-pound levels. Such an audible horn is a natural patient fright-producer, and is thus a severe drawback of the prior art KT 1000.TM..